The present invention relates to occupant position and type sensing systems and methods.
Occupant type and position detection is an important technology for air-bag active restraint technology. Detecting occupant position within a vehicle is important for disabling active restraint devices, such as airbags, when such devices could endanger an occupant. For example, such technology may be used to prevent danger to out-of-position occupants, and certain types of car seats, such as a rear-facing infant seat. Numerous techniques have been proposed, ranging from weight-sensing, range finding using light or sound, electrostatic fields, thermal imaging, or visual pattern recognition, and a brief review of the conventional technology is presented below.
Weight-based sensing relies on load cells or pressure sensors mounted between the seat and floor of a vehicle, or within a seat cushion. Problems with weight-based sensing include effects of seatbelt cinching with car seats and rear-facing infant seats, requiring the use of additional sensors to detect this load. Out-of-position occupants also provide an exceedingly wide variety of weight patterns on any type of sensor or sensor array, making distinction between various categories a very challenging task. Occupants whose feet are on the floor or are raised will have vastly different sensed weights, yet may require the same treatment from the restraint technology. Vehicle bounce, occupant bounce, heavy objects in a seat, and many other complications make this technology very difficult to realize, although system costs can be kept very low.
Ranging systems using ultrasonic time-of-flight sensing such as is disclosed in International Patent B60R 21/16 by Breed can provide a quasi-one-dimensional profile of the occupant. However, this requires either many beams, with attendant high costs, or a scanning beam, with reliability risks and noise issues related to the motor required. Physical parameters of the cockpit space affecting the speed of sound, such as temperature, humidity, dust, thermal gradients, and other disturbances provide significant technical challenges, requiring additional compensation methods.
Sound-based ranging also has a lower limit on the rapidity with which changes to the occupant position can be detected. Environmental noise from normal events like loud music, jangling keys, wind noise, and so forth, can easily dominate the ultrasonic signal, affecting the signal-to-noise ratio, and providing spurious signals, leading to possible false alarms. Poor reflection from ultrasonics on many types of fabrics, or angles of fabrics, causes significant loss of signal, so that the sensor system is blind to many important cases. The wide range of possible occupant positions, types, coverings, and the like, make a quasi-one-dimensional algorithm with 100% recognition capability across all requirements very demanding, requiring costly memory and processing overhead.
Ranging using triangulation with infrared light beams disclosed in U.S. Pat. No. 5,785,347 by Adolph. et al., provides a quasi-one-dimensional profile, similar to an ultrasonic method. Light beams can be sensed more quickly, and can be made less susceptible to environmental noise. Poor reflection and shadowing are serious problems with this technique, as many materials absorb or scatter infrared signals. The cost of an infrared system tends to be high since a plurality of optical devices are needed, and must be aligned properly, often at difficult angles for a manufacturing process. Unlike ultrasonic technology, where the same device operates as transmitter and receiver, the infrared system requires aseparate light source and light sensing device.
Electrostatic occupant detection disclosed in U.S. Pat. No. 5,802,479 issued to Kithil, et al. is a simple concept, relying on the relatively high moisture content of a human body to provide a capacitance signal to a suitable sensor or array of sensors placed to locate an occupant. The electronics and algorithm are very modest, and the resolving capability depends on the number of sensors used. Also, external electromagnetic noise sources can interfere with the operation of this system, and many dielectric and metallic objects that appear in vehicle cockpits can cause faulty signals. Electrostatic detection is often used as an adjunct technology to ranging or pattern recognition systems.
Optical pattern recognition holds promise for occupant detection. However, system costs associated with optics and image processing hardware and software are considerable higher and more difficult than ranging or weight-based sensing. Wide variations in lighting levels and contrasts make this job more difficult in the environment seen by a vehicle cockpit. Sensitivities and degradation due to surface film accumulation can affect the system response over time. From the two-dimensional image produced, the software must detect not only edges, but compare patterns with existing templates, stored in memory. This is expensive, and suffers from shadowing effects, and suffers from the wide variation of objects and positions possible in a vehicle interior. The potential for performance with optical pattern recognition is greater than ranging or electrostatics, but until component costs are considerably cheaper and software techniques more advanced, this will remain unfavorable for high volume applications.
Accordingly, it would be advantageous to have occupant position and type sensing systems and methods that overcome the limitations and disadvantages of conventional systems and methods.
The present invention provides for holographic occupant position and type sensing systems and methods that may be used in vehicular applications, and the like. An exemplary system comprises a light source that generates a pulsed light beam. A beam splitter separates the pulsed light beam into reference and object beams.
A holographic template comprising a plurality of phase patterns receives the reference beam and a reflected object beam that is reflected from an object. Interference between the reference beam and the reflected object beam interact with phase patterns present on the template, and convolution between the beam interference and the phase pattern produces a spot of light when there is an exact match. The brightness of the spot indicates the degree of match and the location of the spot indicates the spatial location of the object.
A two-dimensional detector array detects the magnitude and location of the spot and for outputting signals indicative thereof. A processor processes the signals indicative of the magnitude and location of the spot to generate an output signal indicative of the position of the object and a classification of the object as one of a predetermined number of types of objects.
The method of occupant position and type sensing in accordance with the present invention uses a holographic template to hold a Fourier transform of various images to be recognized. By convolving an interference pattern of the target with this template, a simple charge-coupled device imaging array or CMOS imaging device rapidly determines type and position in a plane of a three-dimensional object.
The system, which is preferably mounted in an overhead console of a vehicle, scans a three-dimensional surface, thus providing two-dimensional information about an object. This is very important, since the location in a plane of an occupant, car-seat, or other object can have almost any location. Processing of raw two-dimensional information is greatly facilitated by the use of the template, wherein numerous images can be stored simultaneously.
The templates, once created, can be mass produced at very low cost, thus providing a very high ratio of information content to component cost. Because of the method of optical processing used in the present invention, the computation requirements for the system are very modest, and the determination of position and class can be made very quickly, faster than ultrasonic or vision-based optical pattern recognition.
There are no moving parts in the system, and optical alignment requirements are very modest compared to infrared or optical pattern recognition systems. Because laser light is highly monochromatic, filters can easily remove any environmental light noise. A key feature of holography is that loss of signal, dust particles, surface films, and other sources of degradation cause a graceful decline in detection, since holographic information is distributed across the media. This is an important advantage over each of the prior art methods described in the Background section. Overall, the present holographic sensing system and method offers high performance with low cost and high reliability, thus meeting the need for vehicle systems in a wide variety of applications, including occupant position and type sensing for active restraint technologies.